/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.spark.util

import java.io.{Externalizable, ObjectInput, ObjectOutput}

import com.clearspring.analytics.stream.cardinality.{HyperLogLog, ICardinality}

/**
 * A wrapper around [[com.clearspring.analytics.stream.cardinality.HyperLogLog]] that is
 * serializable.
 */
private[spark]
class SerializableHyperLogLog(var value: ICardinality) extends Externalizable {

  def this() = this(null)  // For deserialization

  def merge(other: SerializableHyperLogLog) = new SerializableHyperLogLog(value.merge(other.value))

  def add[T](elem: T) = {
    this.value.offer(elem)
    this
  }

  def readExternal(in: ObjectInput) {
    val byteLength = in.readInt()
    val bytes = new Array[Byte](byteLength)
    in.readFully(bytes)
    value = HyperLogLog.Builder.build(bytes)
  }

  def writeExternal(out: ObjectOutput) {
    val bytes = value.getBytes()
    out.writeInt(bytes.length)
    out.write(bytes)
  }
}
